Method of treating the heat-responsive elements of thermostats



ly 1,1942. E. K. CLARK Em 2,288,188

METHOD OF TREATING THE HEAT-RESPONSIVE ELEMENTS OF THERMOSTATS Filed Nov. 22, 1940 FIG- FIG- 2- WITNESSES:

' INVENTOR EA/PL K. CLARK 67 GEORGE f. re ca BY Wflfi} ATTORNEY Patented July 7, 1942 METHOD OF TREATING THE HEAT-RE- SPONSI VE ELEMENTS OF THERMOSTATS Earl K. Clark and George n. Price, Mansfield, '-0hlo, assignors to Westinghouse Electric &

:-Manufacturing Company, East Pittsburgh, Pa.,

a corporation of Pennsylvania Application November 22, 1940, Serial No. 366,786

' 4 Claims. (Cl.148- 6) Our invention, relates to thermostat structures of the expansible or volatile-fluid type and has for an object to provide an improved method of l treating the heat-responsive elements of apparatus of this kind. V

A further object of the invention is to provide more sensitive thermostatic apparatus of the type set forth whichmay be readily produced in large. substantially uniform quantities.

. A still'further object of the invention is to improve the heat-absorbing and heat-radiating properties of the heat-responsive elements of fluid-type thermostats."

These and other objects are effected by our invention as will be apparent from the following description and claims taken in accordance with the accompanying drawing, forming a part of this application, in which:

Fig. 1 is a diagrammatic view of an oven, the temperature of which is controlled by a thermostat constructed and treated in accordance with our invention; and,

Fig. 2 is an enlarged view of the bulb or heatresponsive element of the thermostat.

In the drawing, a heat insulated oven space is diagrammatically shown at Illand heated by an element H which we have shown of the 'electrically-energized type. A thermostat of the expansible fluid type is shown generally at I! and includes a switch i3 arrangedwithin a casing I4 exteriorly of the oven and controlling a circuit I5, the latter including the heating element II. The circuit 15 is connected to a suitable source of electrical energy (not shown) as is well understood.

Operation of the switch 13 is effected by an expansible and contractible element l6, such as, for example, a bellows. The bellows is connected by a relatively small tube [1, commonly referred to as a capillary tube, to a bulb or reservoir l8 arranged in heat transfer relation with the heated air in the oven space H). A suitable expansible liquid is contained in the bellows l6. tube l1 and bulb l8, which liquid retains its liquidity at temperatures up to 650 F. and which expands and contracts as its temperature is increased and decreased, respectively.

As the operation of the apparatus referred to heretofore is well understood in the art, no description thereof is deemed necessary. Fluidtype thermostats which have been employed heretofore for controlling ovens of electric ranges have not been sufficiently sensitive to meet requirements now imposed by certain utilities and testing laboratories. These prior art thermostats have, in general, been unable to maintain oven temperatures within a 40 F.- amplitude, the figure which now represents the maximum amplitude permitted by such utilities or testing; laborat-ories; The thermostats provided heretofore have their fluid-containing bulbs formed of copper or other metal, and, when new, have such low heat-absorbing and heat-radiating capacities that a relatively large differential obtains between the oven air temperature and fluid temperature. In other words, changes in the temperature of the fluid lag behind temperature changes in the oven air so thatthe temperature differential of the ovenair is higher than the figure now required. A further disadvantage of these prior thermostats is that the heat-absorption capacity of the thermostat changes with use or as the surface ofthe bulb becomes oxidized. This change in heat-absorbingcapacity usually necessitates a visit of the service man, after a period of use, for adjustment of the thermostat.

In accordance with our invention, we treat the bulb of the thermostat prior to'its application to the apparatus to be controlled, so that the heatabsorbing and radiating qualities of the bulb are materially increased and so that substantially no change in these qualities obtains during extended use of the thermostat. We first etch the surface of the bulb for materially increasing its area and then blacken by an oxidation reaction the etched or matted surface of the bulb. Preferably, the smooth metal bulb is cleaned in a vapor degreaser for removing oil or grease spots and the bulb is then acid etched by dipping for two to five minutes in a} solution of four parts muriatic acid, one part nitric acid and one part water. We have found that the suface of the bulb may be increased to 300% of its original surface when so treated. The bulb is then rinsed in clear water and may be blackened or oxidized by dipping from ten to thirty seconds in a poly-sulphide and water solution. During the latter step the bulb should be dipped just long enough for obtaining a blackened surface, as an excessive time in this dip may cause flaking. After the oxidizing process, the bulb is rinsed in clean water and then suitably dried.

While we prefer to employ the described method of roughening the bulb for increasing its surface area, it will be understood that this step may be effected other than by an acid etching operation. For example, the bulb may be roughened for increasing its surface area by sandblasting or other mechanical means. The finally treated and blackened bulb I8 is shown in Fig. 2.

We have found that the maximum temperature amplitudes in ovens" controlled by thermostats treated in accordance'withpur invention have:

been materially reduced to a value offthe. order of 27 F. when measuredv with a" bare thermocouple disposj'edi ext-the: center ofi;thet rangeipveng Furthermore," we" so treated does not varymaterially whenin ser vice, so that adjustment or-calibration. f the',

thermostat after a period of' useisgnothecessar From the foregoing it will we have provided improved t ratus of the fluid type where; e materially increased and wh'reinfvariation operation after an extended peribdofuseare obviated. Furthermore; the operatiomof'the'liea-tei-'1 have found th-at the heatiab i- 'sorbing and heat-radiatingpapacity of. the bulbs be apparent that I responsive element", when" producedin, large v quantities is justmeht a: readily effect tant" teature" of j i i-b3. 'librationfof-the thermostat. could? only b1 litalned after "ma y and widely different; a

cost

statsvo f t 'ermos a ""pro'per adjustment; a. 11W ile we have fsho'wn our inventionairrv uti the art'that it is n ot'so limited-,'=but=is susceptible of various otherchangesand modifications.with-r thereof and we- 'out' departing from the- 'spirit desire; therefore; that enly" "such: limitations shall be placed thereupon-as 'ar'ei ior thjf in, the appended claims; e c a m' a 1; ,IIfhe; method. "or mel ing athermostat: of? the h the'armostaticstructure.z iszmorer We consider." this man." import: '3 our inventionas; in the past, the; and radiating capacities :of: um; ave vari'd so widely? thatq the The non unlformity' 0f the: .z-bulbs etofor'e' hasftherefora:increased the; of produci'iig uniform thermo- I; type and has-been-the cause" of mg* necessary i tomaintaim ;the

ne sfbr it' ill-beobvioust'o-'those -skilledirinspecificallyset 40 uniform, so that the originala'dimined coating of a; compound; n he-bu b whi tia fluid type for aheatedappliance, which: thermostat embodies a thermostatic bulb-formed of: a; metal which I progressively-9 oxidizes-z inwsaida appli. ance over; an extendedi periodi of time soithatv its heat-absorbing property increases during such-. -per iod saidi bulbn containing; a.v temperature-gresponseg fluid; yv'i the step of providing theibulb-g1, prior" to the absorbing property which i'snot substanaltered during use; inthe heatedi appliance. 2:. JI he ;n 1eth0d;ofimaking heatedlappliance,whichther-mor static bulb formedv ofa av Xidizes 1n-v said' ap its h eat'absorbing such period, said-bulbcontaining a temperaturerespon-sive,,- fluid; a which. metho djncludes. the step of}:-applying anioxidijzing SOHlti'OIl-WO the bulb, t'he-therm'ostat' for use prior. to: v the assembly. of in the heated appliance"; o: provide a! predeter- H aid gmetal: on high; heat abl QOlIlpQuIlgk has sorbir gproperty during use in the heateclliappli'ance.

3. The method as plai'med" intheoxjdizing,solutiona iomprises asulphide,

-, ii-ma method r making a; thermostat:- of; the

fluict-v t peigr axhea d5 appliance; which-thermostat embodies a v copper, said bulb containing:

I a. temperatureere sponsive :fluid,

to the-assembly of the. thermostat in the heated.

appliance to provideiv a1 coat in'g on the bulb whose heat absorbingv property is: relatively highand is not substantially heatedqappllance j v, v v I EARL-,K. CLARK. GEORGE E; PRICE.

ch; method. includes,

assembly of; the thermostat for. use inithe heated ance, with a; dja rkt coating having a high.

a thermostat. ofv the property increases during.

thatlisnot: substantially 'a-lteredf claim 2 wherein thermostatic. bulb formed" otl hich-met od includes" the step of applyinga sulphide solution to-the-bulbz prior altered, during usein, the 

